This project is designed to evaluate the feasibility of a visual prosthesis for totally blind individuals by stimulating chronically implanted microelectrodes in the visual cortex. A class 1000 clean room has been constructed in Building 49 for the complete fabrication of microelectrode arrays that will be implanted in primate visual cortex to evaluate reliability of the percutaneous connector system and the safety of the stimulation parameters. During FY1998, two non-human primates were implanted with multi-electrode arrays (<30 electrodes each), using the percutaneous connectors and microelectrode arrays that are designed for use in an eventual human implant. The first primate was implanted for 10 weeks before sacrifice and the second for over four months. Both animals were monitored daily for complications. A protocol of stimulation was applied 5 days per week to designated electrodes in order to provide information of tissue reaction and electrode behavior at various charge carrying levels, up to the range known to be marginal for safety. Neither animal experienced any complications from the implant. Only one electrode became inoperative during the implant periods and there was no sign of mechanical or infection problems with the miniaturized connector pedestal in either animal. Histological analysis of all of the electrode sites involved removal of connective tissue encapsulation around the electrode sites using a special laser ablation system developed at Huntington Medical Research Institute. The individual electrodes removed from each animal are being studied by scanning electron microscopy. The electrode sites themselves will be reconstructed from plastic-embedded 100 um sections from brain tissue blocks. Eevery effort is being made to preserve the integrity of each electrode site, so as to permit reliable assessment of the tissue reaction, if any, at various levels of chronic stimulation intensity. This project will be terminated at the end FY 1999 as an intramural effort. Given the successful tests of the electrode system, particularly the reliability of the pedestal connector, we anticipate that a group outside NIH may be interested in using the approaches and devices developed in LNLC for the first intracortical visual prosthesis designed for indefinite human implant. In anticipation of this, fabrication of a number of electrode arrays designed for human imlplantation will be carried out by LNLC staff in the clean room in Bldg. 49.